1. Field of the Invention
The invention relates to a method and system for ensuring the integrity of at least one computer software program which can be carried out by means of at least one encryption/decryption module, the at least one software program being transmitted, by means of a transmitter, to a decoder which is equipped with the at least one encryption/decryption module by means of a long-distance information transmission network.
2. Description of Related Art
More precisely, the invention relates to a method in which the transmitter carries out:
a) a step for encrypting information signals transmitted to the decoder,
b) a step for transmitting, to the at least one encryption/decryption module of the decoder, a message containing the information required for the decoder to decrypt the information signals transmitted at step a), and
c) a step for transmitting the at least one computer software program to the at least one encryption/decryption module of the decoder,
and in which the decoder carries out:
d) a step for decrypting the information signals transmitted by the transmitter during step a) using the information provided for this purpose in the message transmitted during step b).
Methods of this type are, for example, required in payment-based systems for broadcasting television channels. In these systems, in order to update the decoders, the transmitter frequently broadcasts corrective software programs which are intended to be carried out by each of the decoders in order to update the functionality thereof. A corrective software program is a small program which can be carried out by an electronic computer and which is intended to modify specific parameters or parts of a larger program which can be carried out by the same computer. These corrective software programs are also known in English as “patches”.
In conventional manner, each decoder is equipped with an encryption/decryption module which is capable of encrypting and/or decrypting the signals transmitted by the transmitter in order to decrypt the television channels transmitted. This module is conventionally referred to as a security module since it serves to secure the information exchanges between the transmitter and the decoder. This encryption/decryption module is also capable of carrying out the corrective software programs which it receives.
The encryption/decryption module is in the form of an autonomous module. For example, this encryption/decryption module is nowadays integrated in a chip card which must be inserted in the decoder in order for the decoder to function correctly.
Nowadays, there are a number of decoders which have been fraudulently constructed in order to receive payment-based television channels without paying. These decoders are referred to as pirate decoders. Since the encryption/decryption part of the signals received is the most complex, these pirate decoders most often integrate an authentic encryption/decryption module which is associated with a fraudulent device for controlling this module. The fraudulent control device transmits to the authentic encryption/decryption module the information it requires for decrypting the payment-based television channels, even if the information has been acquired in a fraudulent manner.
In order to combat pirate decoders of this type, the solution has for some time consisted in broadcasting, via the transmitter, special corrective software programs referred to as anti-pirate programs. These anti-pirate corrective software programs are intended to modify the operation of the authentic encryption/decryption module so that the pirate decoder as a whole becomes unusable. An anti-pirate corrective software program, after it has been carried out by the authentic encryption/decryption module, may, for example, modify the location of the memory zones in which the information decrypted by the authentic encryption/decryption module is stored, or seek the information required for decrypting television channels in another memory location.
However, the most recent pirate decoders are now capable of removing the anti-pirate corrective software programs before they are received by the authentic encryption/decryption module. The anti-pirate corrective software programs are thus not carried out by the authentic encryption/decryption module.
The object of the invention is to overcome this disadvantage by providing a method in which it is made more difficult to remove a software program transmitted to a decoder.